This invention relates to optical fiber couplers with attenuation, particularly variable attenuation and more particularly to a centrosymmetric spherical reflector-type optical fiber coupler.
Centrosymmetric reflective (CSR) technology employs concave mirrors to couple the output of one of one or more optical fibers into one or more other optical fibers. A CSR device uses a concave sphere-segment reflective surface such that an object placed in a plane perpendicular to the symmetry axis of the spherical segment and containing the center of curvature images the object on the opposite side of the axis equidistant from the center of curvature. The imagery is completely achromatic, mode insensitive and diffraction limited so long as the object and image are not too far from the axis of the reflector. Representative CSR devices are disclosed for example in U.S. Pat. Nos. 4,934,784 issued Jun. 19, 1990 and 4,329,017 issued May 11, 1982 in the name of Kaptron, Inc. of Palo Alto, Calif.
It is useful to control the coupling between pairs of optical fibers in a CSR device. What is needed is a mechanism for controlling the coupling without affecting the mode distribution in the fibers.